1. Field of the Invention
This invention relates to a ceramic precursor composition, a ceramic green sheet, a method for the production thereof, a ceramic sheet, and use thereof. More particularly, it relates to a zirconia or alumina ceramic precursor composition, the ceramic green sheet, a method for the production thereof, and ,use of the ceramic sheet.
2. Description of the Prior Art
The doctor blade method is a method for producing a ceramic green sheet by mixing a ceramic powder with an organic solvent, a dispersant, a plasticizer, a binder, etc. thereby preparing a slurry, casting the slurry in a regulated thickness on a carrier film with the aid of a doctor blade, and drying the .applied layer of the slurry. This method has been commercialized by regulating the ceramic powder as the raw material in particle diameter and particle diameter distribution and using a butyral type resin like polyvinyl butyral, a cellulose type resin like ethyl cellulose, or polyvinyl alcohol as the binder.
When this conventional binder is used, however, since the formed green sheet is deficient in flexibility, it has the possibility of sustaining a fructure or a crack while it is being dried or punched or otherwise handled under an impact. The method, therefore, has no alternative but to use such a plasticizer as a phthalic ester and inevitably has a disadvantage that while the formed green sheet is kept in storage, the plasticizer eventually exudes to and volatilizes from the surface of the green sheet and leaves the green sheet in an embrittled state. The binder has poor thermal decomposability. The ashes such as carbon and Na which remain after the green sheet is purged of the binder possibly cause deformation of the green sheet as with blistering, crazing, and cracking during the course of calcination. When the green sheet is used as electronic parts such as IC substrates, IC packages, and dielectrics, the deformation impairs the electric insulating property and other electric properties of the electronic parts. Further, the ashes form a cause for rough surface and low sintering density. Particularly in the production of a thin sheet contemplated by the present invention, the ceramic powder as the raw material is desired to comprise submicrons not exceeding 1 micron in diameter. When the conventional binder is used, it tends to induce aggregation of such ceramic submicrons. For the formation of the sheet, the binder must be used in a large amount. All these adverse factors aggravate the deficiency in formability of the green sheet.
An object of this invention, therefore, is to provide a novel ceramic precursor composition, the ceramic green sheet, a method for the-production thereof, a ceramic sheet, and use thereof.
Another object of this invention is to provide a zirconia or alumina ceramic precursor composition, the ceramic green sheet, a method for the production thereof, the ceramic sheet, and use thereof.
Yet another object of this invention is to provide a ceramic precursor composition capable of forming a green sheet possessing sufficient mechanical strength and flexibility, excelling in surface smoothness, and having a uniform thickness of not more than 0.5 mm, preferably not more than 100 microns, a ceramic green sheet formed of the composition, a method for the production of the ceramic green sheet, a ceramic sheet obtained by calcining the ceramic green sheet, and use of the ceramic sheet.